A solar cell is a device that is capable of converting sunlight into electrical energy by the photovoltaic effect. A solar cell, such as a multijunction solar cell, can have one or more p-n junctions that are sometimes referred to as subcells. These junctions may be connected in series to form a multijunction solar cell but may also be connected in other electrical configurations, such as in parallel, or in a combination of series and parallel connections.
The interest in solar cells has been increasing due to concerns regarding pollution, energy security, and limited availability of other energy sources. This interest has been for both terrestrial and space applications. In space applications, solar cells have been in use for many years and the development of higher efficiency solar cells allows increased payload capabilities. In terrestrial applications, higher solar cell efficiency for conversion of the sunlight into electrical energy results in a smaller cell area required for a given electrical power output, and therefore lower cost per watt and greater cost effectiveness.
However, solar cell fabrication processes are prone to introducing various defects into solar cell structures, such as the interface between a multijunction stack and a substrate, which may render the cells unsuitable for operation. The defects can be reduced to a certain extent by various process control measures, which add significant costs and delays to fabrication of the solar cells. It has been found that some defects, if detected and treated, can remain within the solar cells without impacting performance of these solar cells.